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How low can you go?


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I am having one of those Zen moments, or what drunks call a moment of clarity. Possibly.

 

We seem to obsess about reproduction of frequencies we cannot hear, but many are content with speakers that only go down to 50 or so Hz. Even my (modest) sub only takes me to 28Hz. Some classical music will go down to 16 Hz, and we uncontroversially hear at least to 20 Hz, and feel significantly lower frequencies than that.

 

So why not obsess on the low frequencies?

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So why not obsess on the low frequencies?

 

As long as you realise that those low frequencies aren't pure sine waves, and often have VERY fast rise times initially. Some may even be surprised at the degree of audible improvement achieved by DC coupling the input of a preamp/ Power amplifier, even though your speakers may be only good to 35Hz.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

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I've always felt the bottom is crucial to convincing sound.

I've known engineers who filter frequencies from individual instruments when they feel they are not part of the instrument's range.

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My contention is that even a piccolo needs that *low* bottom to sound natural.

It all starts at the bottom.

(My mics of choice are down 1 dB at 4 Hz.)

And in real life it is stereo (going to what you said Alex, about wavefronts - though you referred to is as rise time).

 

And I've long said that one of the greatest benefits of 24/192 audio is how natural the bottom sounds.

 

Best regards,

Barry

Soundkeeper Recordings

The Soundkeeper | Audio, Music, Recording, Playback

Barry Diament Audio

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I am having one of those Zen moments, or what drunks call a moment of clarity. Possibly.

 

We seem to obsess about reproduction of frequencies we cannot hear, but many are content with speakers that only go down to 50 or so Hz. Even my (modest) sub only takes me to 28Hz. Some classical music will go down to 16 Hz, and we uncontroversially hear at least to 20 Hz, and feel significantly lower frequencies than that.

 

So why not obsess on the low frequencies?

 

 

I completely agree. The willingness of so many audiophiles to give up on, or not really care about low frequencies has never made any sense to me.

Speakers: Melco N1A/2 | Denafrips Gaia | Denafrips Terminator Plus/Lampizator Golden Gate | Jeff Rowland Coherence II Series 2 pre | Blue Circle Audio BC-202 amp | Raidho XT-1 | Revel B112 subs  

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I am having one of those Zen moments, or what drunks call a moment of clarity. Possibly.

 

We seem to obsess about reproduction of frequencies we cannot hear, but many are content with speakers that only go down to 50 or so Hz. Even my (modest) sub only takes me to 28Hz. Some classical music will go down to 16 Hz, and we uncontroversially hear at least to 20 Hz, and feel significantly lower frequencies than that.

 

So why not obsess on the low frequencies?

 

 

That's a good question. We used to (by "we", I mean the general population). Back in the 1930's through the 1950's, people obsessed over low-end response. In fact, during the "golden age of radio", the ultimate household status symbol was the huge console radio receiver in the living room (or parlor, to which it was often referred). This radio would ideally have a 12" speaker, at least a 5-watt amplifier (!), and be multi-band (AM, short-wave, and sometimes "police band". Starting in the late 1930's many also had FM, albeit in the 50-70 MHz band which was obsoleted after the war in favor of our current 88-108 MHz band. Some, from manufacturers such as E. H. Scott, MacMurdo, Stromberg Carlson, et al actually had separate bass and treble controls, as early as the mid '30's, but most just had a "tone" control. Today we would call a tone control a "high-cut" control or a treble attenuator. Practically everybody kept that control turned all the way down to attenuate the highs as much as possible! According to the book From Tinfoil To Stereo by Welch and Reed, "tone tests" were carried out in the late 1930's by such august organizations as Bell Labs and RCA Labs under the late Harry F. Olsen. In England, similar tests were conducted by the BBC under the auspices of Alan Blumlein, Reg Williamson, et al. The results were universal. People liked bass, and cared nothing for high-frequency reproduction. This is possibly because most people used their radios only for radio, which was, by definition, AM. Not only was AM frequency response restricted to between 5 KHz and, in rare instances, 10 KHz, but it was accompanied by that bane of the broadcast world, static. Also, the amplifiers used were often fairly high in distortion as was the audio part of the broadcast equipment. Keeping the treble fully attenuated reduced the apparent high-frequency distortion, and kept the static at bay as well. If the radio was also a phonograph reproducer, then again, high-freqency content was restricted - at least until the advent of the LP. Also 78's tended to have high-amounts of surface noise. If you ant for whatever highs were present, you had to listen through a curtain of rushing noises and hiss. After the war, British Decca (known Stateside as London Records) introduced it's 'FFRR' process whereby some 78's had extended high-frequency response to 14 KHz. The problem was that most pickups available couldn't either reproduce the FFRR frequency extension, or in many cases, couldn't even track it! Add to that the fact that few consumers paid any attention to the admonition that they replace the steel "needle" after every play, and you have records that were all but destroyed after a few plays with a worn steel stylus. The high-frequency distortion soon became so high, that it was no wonder that people kept their treble fully attenuated all of the time. But, while these are all good, legitimate reasons for attenuating the high-frequency response of reproduced music, the actual fact was that it was the fashion of the day. I had an uncle who had a magnificent RCA Victor radio-phonograph. It had a 12" woofer and a 3" tweeter and both speakers were housed in a bass-reflex cabinet sitting on springs inside the main furniture cabinet. My uncle used to brag that his pickup had a diamond stylus (an expensive luxury before the era of artificial diamonds) and his 78's were rare in that he took exceptional care of them and with the diamond stylus they were not gouged like most. The RCA also had modern FM on the dial (it was a 1948 model), so he had access to real high-fidelity content. Yet he too, kept the treble control fully attenuated and the separate bass control boosted all the way. The thing went BOOM-boom-boom all the time. When I was visiting (as a teenager) I would set the tone controls to flat, and whether playing my uncle's FFRR classical 78's or the FM, I thought the thing sounded magnificent and wished that my record player at home sounded as good.

 

Even after the hi-fi craze became the rage after the war, people still obsessed over the low end. By that time most hi-fi enthusiasts realized the top-end was as important as the low end, and tweeters became de-rigur, but, still that elusive bass, was still prized by audiophiles. It was still pretty elusive. Even big "professional" speaker systems from Altec Lansing, RCA, Bozak and Electro-Voice still couldn't get much below 50 Hz. In the early 50's Electro-Voice introduced a huge speaker system called a "Patrician" with a thirty-inch woofer! This is what was needed to get down below 30 Hz in those days. I've heard a system built around a pair of Patricians, and while the quantity of bass is prodigious, the quality of bass - not so much. These big woofers were slow, flabby, tubby, and boomy. It took Edgar Vilchure's Acoustic Research Corporation and the AR-1 "acoustic suspension" speaker to revolutionize the quest for good low-end. After that, people's attention shifted upward in the spectrum.

 

I think that reason people aren't so fixated on bass performance any more is simply because decent quality bass below 50 Hz is easy to come by, and such a small percentage of the content of music falls in that last octave or so, that people just don't find the pursuit of that end of the spectrum that compelling any more. I must say, however, that the best bass reproduction that I've ever heard from a stereo system was at a really old guy's house. This fellow was turning over the recording of a local symphonic wind ensemble to me, and he wanted me to hear some of his stuff. His speakers were Altec Lansing. They consisted of huge cabinets each containing four 15" Altec Lansing drivers for a total of eight! I've never heard a room so bass-loaded by a speaker system before! It was truly spectacular. Unfortunately, this magnificent bass crossed over to a pair of Altec 500 Hz "treble horns" and there the magic stopped. These aluminum horns sounded awful - always did.

George

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At last year’s Capital Audiofest, Brian Zolner (owner of Bricasti) demonstrated to me while we were in the Tidal room how the accurate reproduction of very low frequency truly brings classical music a level of realism I have never experienced. I am not talking about the big boom of kettle drums but just the natural acoustics of the massed instruments & the hall. It was a cathartic experience for me. I guess I should get out more?

Bill

 

Practicing Curmudgeon & Audio Snob

 

....just an "ON" switch, Please!

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I think that reason people aren't so fixated on bass performance any more is simply because decent quality bass below 50 Hz is easy to come by, and such a small percentage of the content of music falls in that last octave or so, that people just don't find the pursuit of that end of the spectrum that compelling any more. I must say, however, that the best bass reproduction that I've ever heard from a stereo system was at a really old guy's house. This fellow was turning over the recording of a local symphonic wind ensemble to me, and he wanted me to hear some of his stuff. His speakers were Altec Lansing. They consisted of huge cabinets each containing four 15" Altec Lansing drivers for a total of eight! I've never heard a room so bass-loaded by a speaker system before! It was truly spectacular. Unfortunately, this magnificent bass crossed over to a pair of Altec 500 Hz "treble horns" and there the magic stopped. These aluminum horns sounded awful - always did.

 

I never found a love for bass until I started using 15" OB woofers. Now I use four of them in stereo and things are really articulated in the low range. I find most subs to be a bit boomy…they tend to "load" the room unnaturally for me. I don't get this effect at similar volumes with open baffle. I also found I liked the bass better when I switched to AMT tweeters. They really let me hear the bass in new ways (plucks are much more real, bass drum peddles hitting, etc).

 

Best,

John

Positive emotions enhance our musical experiences.

 

Synology DS213+ NAS -> Auralic Vega w/Linear Power Supply -> Auralic Vega DAC (Symposium Jr rollerball isolation) -> XLR -> Auralic Taurus Pre -> XLR -> Pass Labs XA-30.5 power amplifier (on 4" maple and 4 Stillpoints) -> Hawthorne Audio Reference K2 Speakers in MTM configuration (Symposium Jr HD rollerball isolation) and Hawthorne Audio Bass Augmentation Baffles (Symposium Jr rollerball isolation) -> Bi-amped w/ two Rythmic OB plate amps) -> Extensive Room Treatments (x2 SRL Acoustics Prime 37 diffusion plus key absorption and extensive bass trapping) and Pi Audio Uberbuss' for the front end and amplification

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OK I'll bite.

And I wil be quite challenging I think. So skip if you can't bear that kind of thing.

 

IMG_0725b.JPG

 

Open baffle wave guide / horn.

 

 

Orelo MKII Sub-low Response.png

 

This is what I call super straight to 19Hz (officially +/- 1dB as this plot might tell you). And for insiders, no, this is not super smoothed (see the 1/12 oct at the bottom).

 

This tells nothing much if it doesn't come along with the text that this is without audible distortion (2nd and 3rd harmonic to begin with) which I rated empirically found at under 3% THD. The reference level of this speaker - as how it was "set" by me - is 88dBSPL (@1meter). This means that when 88dBSPL is output the THD is under that 3% at all frequencies (the challenging for this is the low end). And for those who don't know : this also means that a frequency of 19Hz up to around 23Hz should not be audible. If it is, audible distortion is your share, since we can not hear 19Hz. Thus if we hear someting after all it means that we hear 38Hz (2nd harmonic distortion). Or 57Hz (3rd). Etc.

 

The challenging about this post is me claiming that not so many will be able to do this.

It takes special drivers to begin with, a special speaker design, and foremost the explicit objective of the designer/manufacturer to achieve it. But also : the sheer idiocy of tuning at "THD" (which I happen to be familiar with from the DAC side of matters). And yes, it all starts with why this would all be so important which in itself needs the experience first. It even needs the relating to what you perceive and what others perceive hence are you crazy yourself or what.

 

All is, and this is a claim too, about how loudspeaker manufacturers will tell you about the speaker going "flat to" 27Hz etc. Yes ? well, measure it. No way it will do it and IF it does, it distorts as hell. Not that you'll perceive that because all what happens is that e.g. a 32Hz organ pipe sounds like a bombastic one which is interesting, but no "flute" (pure sine) as it originally was. You'd need to be in the church when recording happened to really know. And the problem of course is, organs can sound "bombastic" (I mean raw).

 

Same with synthesizer "music" which is the foremost type of music which goes infinitely low if artistically created so. 26Hz happens all the time and what we normally perceive from that is fairly "square" sound. Super nice. But if that was intended to be a sine ... we just would not know ...

 

This is how this is a whole world of its own and for me it took quite some reasoning in advance of how things would be or should be, which I now know in aftermath and it *still* needed reasoning like "is this right ?". Just think of it :

 

Now, at some stage the speaker was finished but it could be perceived as not neutral. Thus, coloring. If I can't stand one thing it is that; tracks from even different albums may show a same nature. This, while the speaker especially should not do that. Also, since all is about measurements in the realm I just talked about, I couldn't get it. But what happens ?

As soon as something plays a sine, well, it sounds as one. Good. But if two very different tracks play a synthesized sine (so from a synthesizer) at the same frequency, it sounds 100% exactly the same. And it should ! It is only that modern synthesizers often are not capable to play pure sines, but those who can now sound the same.

Oops.

 

Point is, and this is what you learn when explicitly working in this field and in this fashion, when distortion is in order in the first place it all depends on the level playing. Of course the level varies all over to begin with (say many times per second) but more level implies more distortion. So for those who can do it : When you play a 25Hz test signal at very low level and your speaker is capable of showing 25Hz, you will see that at highering the level the pitch will change. This is just because (for example) the 2nd harmonic distortion gets louder and it starts to interfere (resonate) with the fundamental. The more level the more this happens because the more distortion occurring (fundamental rises 1dB but 2nd harmonic rises 3dB). So doing this with 25Hz, the louder it gets the more it will go towards 50Hz. But actually in practice it works somewhat differently :

 

Without my doubt - and if your speaker driver would be able to "move" in the first place when 25Hz is fed, the 50Hz will be audible long before 25Hz gets a chance. This is difficult to explain by words, but 25Hz is already so poorly audible by us humans while 50Hz easily is - that it takes "nothing" to have the distortion audible which vastly overrules the fundamental.

 

Following up on the latter, the next point is that for the somewhat higher frequency we don't notice it any more. For example, 30Hz we can easily hear. Because of that, the possibly overruling 60Hz (and 90Hz etc.) distort all right, but are not noticed as such. Again, how can you tell what the original sound was to be and even with test signals it becomes hard to distinguish. Thus, here we humans can hear the 30Hz so good to begin with that the distortion now is overwhelmed to some larger degree.

What follows from all is that the "trick" to test whether a speaker audibly distorts is letting it play in the inaudible area (~23Hz and down) and if we then hear something after all it can only be distortion. Sadly this needs the speaker to play at 23Hz to begin with ...

 

So do we even know that official "ratings' exist for loudspeaker woofers (the complete speaker for that matter) ? That is set at 7%. So the most officially when a woofer section distorts less than 7% it is good to go. But don't you think that when you listen to that it will be OK.

Of course, no speaker manufacturer deals with that since it is not electricity harmful stuff etc., but it is also no objective. Actually it works the other way around and that "flat to 27Hz" can not work at all. A woofer starts to roll off at ~100Hz and although cabinet design can help out to some extend, such solutions only *add* distortion. Same when the room is aiding (and obviously, when you sit back and think about this).

 

So I see people write "my sub can do 10Hz easily !". Yes, my former 12Hz rated (SVS) subs could do that too. Easily. Well, sub woofers surely can do it, if only the woofer surface is large enough to replicate the original "excursion surface" (displaced air) like that from a kettle drum without implying more than 3% distortion. So without spending a whole long post on that : If a kettle drum would produce 30Hz at 85dBSPL your speaker can replicate that if the woofer surface is large enough to displace the air the kettle drum's skin does at the particular hit, with the notice that as a rule of the thumb the woofer is not allowed to excurt more than ~3mm (one side). If the woofers can produce that 85dBSPL but don't meet those other specs then you will still hear a kettle drum and as loud, but not the same sounding as the original.

So it is daft, but it is just super simple math to see what it takes and it is not just theory only. This is also how this 3x15" (x2) is able to have a totally real drum kit playing through speakers (really indistinguishable from the real thing) including the kick drum. And the very same design speaker with 3x12" (x2) can not do that 100% on the kick drum (the stomach thing).

 

Lastly, and this has been mentioned in this thread already, the real-real thing can only emerge when the ambient response of the recording room/hall/etc. can be reproduced. As far as I have seen this needs up to 20Hz. For example the kick drum plays at some sort of fundamental of 38Hz but it "rolls" up to close to 20Hz because of the room's ambient response. So yes, I have been watching live FFT's from music playback for dozens of hours (if not hundreds). What you also learn from such a thing is how LP is high passed at ~30Hz. That is, looking at CD transfers from the era when LP was the medium. This is also how you learn that MFSL is not always a hoax and that *those* some times are not high passed. Nice example : The Wall (PF version). The start of that goes with 20Hz "rolls" of the big drum. No such thing on the normal CD (not remaster) version. Such a thing makes a recording 100% different from what you were used to.

 

That's all.

Peter

IMG_0725a.jpg

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There's no doubt that low end bass adds to enjoyment of reproduced music. I used to listen to good Booshelves (Sonus Faber) plus a Mirage sub. The Sub was only an "okay" one and only played clean to about 28Hz, although there was obviously output below that. So it was adding something like an octave below what the SF speakers could do cleanly.

 

When the sub was properly setup, you didn't "hear" it directly but you felt it and noticed the effect. All parts of the spectrum, not just the low end , sounded better. In that system I had DRC and a digital crossover splitting the signal between the sub and the bookshelves, so I could do an A/B comparison at the flick of a button. The system with the sub was much better.

 

But it is true that a lot of recorded music has very little or no musical information below about 40hz, so for that music the sub didn't do much.

 

In general my experience is that most people are happy with decently reproduced bass that rolls off somewhere between 50-70 hz. They don't miss the lower notes. Maybe partially b/c they've never been exposed to what they are missing.

 

I stopped using the sub when I got my floorstanders that do a good job reproducing bass into the low 30hz region, and actually produce better quality bass within those limits than that sub.

 

Maybe one day I will get a really good sub and use room correction and re-introduce a sub to the system. I listen in a small room, and even though I have bass traps and acoustic panels installed, I wouldn't want to fill the room with very low bass without having some DRC control.

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The best and most accurate speaker can't do much as soon it is placed inside a room ...

 

So it is most important to "pair" the speaker system with the room, to get a flat (calculated) response to begin with.

 

After that, you will soon run into the room-mode trap(s), which is a story on its own.

 

Thats why I have decided to try and use the speakers I own now, because of their cardioid bass response, which helps a lot with integration. They have a (measured) response down to "only" around 30Hz, but for my room and my needs thats just fine.

Esoterc SA-60 / Foobar2000 -> Mytek Stereo 192 DSD / Audio-GD NFB 28.38 -> MEG RL922K / AKG K500 / AKG K1000  / Audioquest Nighthawk / OPPO PM-2 / Sennheiser HD800 / Sennheiser Surrounder / Sony MA900 / STAX SR-303+SRM-323II

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In my dedicated and treated HT room we would be lost without that feeling or rumble in your chest of that low end bass during movies being driven by 2 JL Audio fathom IWS. I might not be able to hear as low as these subs go, but I do know I can feel it.

The Truth Is Out There

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I think that reason people aren't so fixated on bass performance any more is simply because decent quality bass below 50 Hz is easy to come by, and such a small percentage of the content of music falls in that last octave or so, that people just don't find the pursuit of that end of the spectrum that compelling any more.

 

+1

 

My former speakers could reproduce down to 20Hz. While I would like to still have that last bottom octave when listening to those few recordings where it is present, I wouldn't trade it for the superior sound quality my current speakers produce at all higher frequencies. And they do a good job down to below 40Hz, noteworthy for stand mounted speakers.

"Relax, it's only hi-fi. There's never been a hi-fi emergency." - Roy Hall

"Not everything that can be counted counts, and not everything that counts can be counted." - William Bruce Cameron

 

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  • 4 weeks later...

WG, great topic. I obsess about it. Bass extension accounts for about 3/4 of speaker cost for quality consistent with the rest of the frequency range.

 

And reproduction at very low freqs also distinguishes *source* components very measurably--including DACs! But few builders and no reviewers *measure* down there...and they get phase and amplitude distortion that most equipment passes along but never gets measured. So... bass matters!

 

For heaven's sake, align your subs and bass drivers with the rest. Use your ears. Get them within 1/8" of the right position, by listening. Take your time. It's free, and there is no substitute for that effort.

Mac Mini 2012 with 2.3 GHz i5 CPU and 16GB RAM running newest OS10.9x and Signalyst HQ Player software (occasionally JRMC), ethernet to Cisco SG100-08 GigE switch, ethernet to SOtM SMS100 Miniserver in audio room, sending via short 1/2 meter AQ Cinnamon USB to Oppo 105D, feeding balanced outputs to 2x Bel Canto S300 amps which vertically biamp ATC SCM20SL speakers, 2x Velodyne DD12+ subs. Each side is mounted vertically on 3-tiered Sound Anchor ADJ2 stands: ATC (top), amp (middle), sub (bottom), Mogami, Koala, Nordost, Mosaic cables, split at the preamp outputs with splitters. All transducers are thoroughly and lovingly time aligned for the listening position.

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I settled on subs after switching to powered monitors. The bass was tight, just not extended.

Tried passive crossovers, active, and both fullrange. Was okay.

Found an active crossover with DRC. The way to go. Running passive 3 ways with a sub blended in. All sealed box.

I could never go back to full rangers and no room correction. Or stand alone monitors.

Someday, software will do all this easily. Maybe even today.

Try DRC. It is convincing.

 

2012 Mac Mini, i5 - 2.5 GHz, 16 GB RAM. SSD,  PM/PV software, Focusrite Clarett 4Pre 4 channel interface. Daysequerra M4.0X Broadcast monitor., My_Ref Evolution rev a , Klipsch La Scala II, Blue Sky Sub 12

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For heaven's sake, align your subs and bass drivers with the rest. Use your ears. Get them within 1/8" of the right position, by listening. Take your time. It's free, and there is no substitute for that effort.

I'm all for rational action and experimentation, but I'm having a problem understanding how a driver that puts out pressure pulses with wavelengths of several feet could possibly affect sound quality with less than an inch of shift in physical position or angulation.

 

A 40 Hz tone has a 1/4 wavelength of about 7 feet, so moving it an inch will shift its phase by 1 degree. During the time it takes a 40 Hz tone to span one degree, a 4k tone will go through 100 degrees (a 1% phase anomaly, assuming both tones initiate at exactly the same time, which does not happen even in the best of bands or orchestras). By the second cycle of the 40 Hz tone, the two are even more disparate.

 

I don't think this matters at all because music lacks perfect phase "coherency". A tight band hits the downbeat pretty closely, but it's simply not perfect. Even theoretically, the only phase commonality in music occurs when multiple instruments hit a note on the same beat, and that only applies to instruments that produce a single note at a time. Guitar and piano chords are not struck with simultaneous perfection. Even the best string section using uniform bowing is not perfectly in synch. Further, the harmonics in even a single note played by a string, horn or reed don't all start precisely when the fundamental is generated. The mass of the resonating materials generating the harmonics of an instrument must be stimulated to vibrate, so they don't even begin to emit overtones for a fraction of a second (a tiny fraction, but certainly at least a degree or two of the full cycle of the fundamental).

 

The speed of sound is about 1100 feet per second. If you sit 7 feet from your speakers, a 40 Hz tone gets from the driver to your ears in about 0.007 seconds and goes through a quarter of a phase cycle before you perceive it. A 4k tone takes the same amount of time to reach you but has already gone through 25 cycles when it hits your tympanic membranes and is not "phase-aligned" with the 40 Hz tone in any way. So the drive to "align" drivers leaves me in the cold.

 

On the other hand, shifting a sub an inch could very well affect room resonances, both by better aligning the wavelength with the axis of the room so specific notes aren't reinforced by wall reflections and by avoiding resonance in some component of the structure (e.g. joist, stud, floor board). But as for "aligning" sub drivers to within 1/8", I don't see how this could possibly affect the sound quality of the music itself (apart from the room).

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I am having one of those Zen moments, or what drunks call a moment of clarity. Possibly.

 

We seem to obsess about reproduction of frequencies we cannot hear, but many are content with speakers that only go down to 50 or so Hz. Even my (modest) sub only takes me to 28Hz. Some classical music will go down to 16 Hz, and we uncontroversially hear at least to 20 Hz, and feel significantly lower frequencies than that.

 

So why not obsess on the low frequencies?

 

Very low frequencies kills endoameba histolytica in the gut, very common where the banana, coffee, pineapple & Cannabis grows...

 

Now I'm on serious in investigation if kills also the Dengue mosquito and a new one that transmit (jitter free) the Chikungunya Virus.

 

Stay alert, if no more news from me, Chikungunya mosquito is immune to very low frequencies.

 

Roch

 

PS/ I had to remove my Zen moments, being alert to mosquitoes!...

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I'm all for rational action and experimentation, but I'm having a problem understanding how a driver that puts out pressure pulses with wavelengths of several feet could possibly affect sound quality with less than an inch of shift in physical position or angulation.

 

A 40 Hz tone has a 1/4 wavelength of about 7 feet, so moving it an inch will shift its phase by 1 degree. During the time it takes a 40 Hz tone to span one degree, a 4k tone will go through 100 degrees (a 1% phase anomaly, assuming both tones initiate at exactly the same time, which does not happen even in the best of bands or orchestras). By the second cycle of the 40 Hz tone, the two are even more disparate.

 

I don't think this matters at all because music lacks perfect phase "coherency". A tight band hits the downbeat pretty closely, but it's simply not perfect. Even theoretically, the only phase commonality in music occurs when multiple instruments hit a note on the same beat, and that only applies to instruments that produce a single note at a time. Guitar and piano chords are not struck with simultaneous perfection. Even the best string section using uniform bowing is not perfectly in synch. Further, the harmonics in even a single note played by a string, horn or reed don't all start precisely when the fundamental is generated. The mass of the resonating materials generating the harmonics of an instrument must be stimulated to vibrate, so they don't even begin to emit overtones for a fraction of a second (a tiny fraction, but certainly at least a degree or two of the full cycle of the fundamental).

 

The speed of sound is about 1100 feet per second. If you sit 7 feet from your speakers, a 40 Hz tone gets from the driver to your ears in about 0.007 seconds and goes through a quarter of a phase cycle before you perceive it. A 4k tone takes the same amount of time to reach you but has already gone through 25 cycles when it hits your tympanic membranes and is not "phase-aligned" with the 40 Hz tone in any way. So the drive to "align" drivers leaves me in the cold.

 

On the other hand, shifting a sub an inch could very well affect room resonances, both by better aligning the wavelength with the axis of the room so specific notes aren't reinforced by wall reflections and by avoiding resonance in some component of the structure (e.g. joist, stud, floor board). But as for "aligning" sub drivers to within 1/8", I don't see how this could possibly affect the sound quality of the music itself (apart from the room).

 

Smart post.......that will unfortunately fall on deaf ears.

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...I don't think this matters at all because music lacks perfect phase "coherency". A tight band hits the downbeat pretty closely, but it's simply not perfect.... ...A 4k tone takes the same amount of time to reach you but has already gone through 25 cycles when it hits your tympanic membranes and is not "phase-aligned" with the 40 Hz tone in any way. So the drive to "align" drivers leaves me in the cold... ....On the other hand, shifting a sub an inch could very well affect room resonances... ...But as for "aligning" sub drivers to within 1/8", I don't see how this could possibly affect the sound quality of the music itself (apart from the room).

 

Bluesman,

 

That's all correct and well-stated, but consider 2 things: 1) the crossover between the lowest-freq driver and the others has a fairly big window which could provide an accurate reproduction of the mic's waveform. No matter what performance "errors" occur, the goal is to best match the driver alignment to the input signal. Yet that driver alignment is sensitive because of the imperfect shape of diaphragms, etc. I agree that 1/8" really is obsessive, let's say 1/4", but 1/8" is where I've stopped with crossover points at 200Hz and now even 55Hz, my current point.

 

2) Even with steep HPF slopes, the sub will have output at 4x the crossover point. For me that becomes 220Hz. That wavelength is ~60 inches so a 1" misalignment creates a phase error of ~6deg at that point. Our ears are extremely sensitive to phase changes (credit Darwin), but you're right, .75 degree is really tight. But experience and feedback from hundreds of listeners have led me to this point. Your point about room reflections is an important part of the equation too. How much, I don't know. But that's a reason why I use almost zero toe-in: the first reflections are more coherent.

 

MEs that I've spoken with, including Bruno Putzeys, concur that phase errors of <2 degrees are audible in the high frequencies... that's under a microsecond! So all of your points make sense, but my experience tells me that psychoacoustics effects happen with these tiny adjustments. Let's not forget that the same kind of phase performance is demonstrated by clocks in ADCs and DACs. What is the audible error in those devices? We are now in the femtosecond range. I shouldn't attempt proof by association, that's junk, but my experience setting up systems with individually adjustable driver enclosures has led me here. If you have detached LF drivers, see what changes make an audible difference.

 

Thanks for your excellent reply.

Mac Mini 2012 with 2.3 GHz i5 CPU and 16GB RAM running newest OS10.9x and Signalyst HQ Player software (occasionally JRMC), ethernet to Cisco SG100-08 GigE switch, ethernet to SOtM SMS100 Miniserver in audio room, sending via short 1/2 meter AQ Cinnamon USB to Oppo 105D, feeding balanced outputs to 2x Bel Canto S300 amps which vertically biamp ATC SCM20SL speakers, 2x Velodyne DD12+ subs. Each side is mounted vertically on 3-tiered Sound Anchor ADJ2 stands: ATC (top), amp (middle), sub (bottom), Mogami, Koala, Nordost, Mosaic cables, split at the preamp outputs with splitters. All transducers are thoroughly and lovingly time aligned for the listening position.

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